This invention relates to a control device for a vehicle which is powered by a fuel cell.
With regard to an electric vehicle which is propelled by the operation of an electric motor, Tokkai Hei 9-191582 published by the Japanese Patent Office in 1997 discloses a system which performs output limitation of the direct current (DC) power supply in order to prevent increase in the temperature of the electric motor. Reduction of the input voltage of the electric motor leads to elevation of its temperature, and to increase in the heat loss in the motor. This prior art reduces the output of the DC power supply in such a case, so as to decrease the input current to the electric motor.
Tokkai Hei 11-220812 published by the Japanese Patent Office in 1999 discloses an electric system which enhances the operational efficiency of the electric motor by keeping the input voltage to the electric motor at a constant potential level by output voltage control of the DC power supply.
In connection with the former art, limitation of the output of the DC power supply amounts to a limitation of the output of the electric motor, and as a result the power performance of the vehicle is reduced.
In connection with the latter art, the following problem arises in the case of application to a fuel cell powered vehicle.
For a fuel cell vehicle in which the fuel cell device and a rechargeable battery are connected in parallel to the electric motor, it is desirable to control the output of the fuel cell device at high efficiency in order to balance the charge amount and discharge amount of the rechargeable battery. However, keeping the input voltage to the electric motor at a constant potential level makes this kind of control difficult, and risks increasing the fuel consumption of the vehicle.
It is therefore an object of this invention to prevent excessive rise of the temperature of the electric motor used for a fuel cell vehicle, while restraining increase in the fuel consumption of the fuel cell power plant.
In order to achieve the above object, this invention provides a control device for fuel cell powered vehicle which is driven by an electric motor to which a fuel cell power plant and a rechargeable battery are electrically connected in parallel. The device comprises a converter which converts an output voltage of one of the fuel cell power plant and the rechargeable battery, a temperature sensor which detects a temperature of the electric motor, and a programmable controller programmed to control an output voltage of the converter according to the temperature of the electric motor.
This invention also provides a control method for a fuel cell powered vehicle which is driven by an electric motor to which a fuel cell power plant and a rechargeable battery are electrically connected in parallel. The method comprises detecting a temperature of the electric motor, and converting an output voltage of one of the fuel cell power plant and the rechargeable battery according to the temperature of the electric motor.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.